Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
In a typical cellular wireless communication system, the air interface between a base station and served wireless communication devices (WCDs) may define a downlink (or “forward link”) for carrying communications from the base station to the WCDs and an uplink (or “reverse link”) for carrying communications from the WCDs to the base station. In various implementations, these links may be defined on one or more carrier frequencies or blocks of frequencies. Furthermore, on each link, various channels may be defined through techniques such as time division multiplexing, code division multiplexing, and/or frequency division multiplexing.
In one implementation, the downlink and uplink may each be divided over time into a continuum of timeslots for carrying communications between the base station and the WCDs. WCDs may be arranged to transmit data, such as bearer traffic (e.g., user data) and control signaling (e.g., access requests and the like), to the base station in such timeslots on the uplink, and the base station may be arranged to transmit data, such as bearer data and control signaling (e.g., paging and other overhead messages) to the WCDs in such timeslots on the downlink. Further, the base station or associated equipment may dynamically schedule transmissions of data in particular timeslots, and the base station and WCDs may transmit according to that schedule.
To help overcome errors that may arise in wireless data transmission, the base station and served WCDs may also be arranged to apply a hybrid automatic repeat request (hybrid-ARQ or HARQ) process. In such a process, when a WCD transmits a data packet to the base station, the WCD may repeatedly attempt transmission of the packet to the base station in sequential (e.g., interlaced) timeslots, until the base station confirms that it successfully received the packet or until the WCD completes a maximum number of attempts without receiving such confirmation.
In practice, for instance, the WCD may add more error correction with each subsequent attempt and/or may transmit various portions of the packet with various error correction coding in each subsequent attempt, in an effort to have the base station ultimately receive enough data to constitute or facilitate uncovering the packet as a whole.
During this packet transmission process, the base station may transmit an HARQ message to the WCD in response to each transmission attempt from the WCD. In particular, for each transmission attempt that does not result in the base station having successfully received or uncovered the complete packet payload, the base station may transmit to the WCD on the downlink a negative acknowledgement (NACK), to prompt the WCD to engage in a next transmission attempt. On the other hand, if and when the base station received and uncovered the complete packet (e.g., the packet transmission and any associated decoding by the WCD was successful), the base station may then transmit to the WCD a positive acknowledgement (ACK), to inform the WCD that transmission of the packet was successful, thereby completing transmission of that packet.